In the field of lubricating oil additives, it has been known for many years that various polymers and copolymers can be used as additives for improving a number of the desirable characteristics of these lubricating oils. For instance, certain of these additives have been found to be useful for improving the viscosity index or the rate of change of viscosity of various oil compositions with changes in temperatures, and/or for improving the pour point of lubricating oils, that is lowering the temperature at which they lose their flow properties, as well as other such lubricating oil properties. In particular, it has been known for many years that various polymers and copolymers of acrylate esters, and polymers and copolymers of alpha-beta unsaturated polycarboxylic acid esters have potential utility for such purposes. These compounds, and particularly the copolymers of vinyl acetate and dialkyl fumarates, have been found to be particularly useful for such purposes. Thus, these fumarate vinyl acetate copolymers have been used commercially as lubricating oil additives, primarily because of their ability to act as lubricating oil flow improvers. These compounds can also be used as wax crystal modifiers, such as cloud point depressants for diesel fuels, and as flow improvers for middle distillates and heavy fuels.
In particular, it is shown in Cashman et al, U.S. Pat. No. 2,825,717, that these additives can be produced by the copolymerization of certain polycarboxylic acid esters, and most particularly fumaric acid diesters and maleic acid diesters, with other polymerizable materials, such as vinyl compounds, and most particularly vinyl acetate, in the presence of a peroxide catalyst, in an alkaline medium. The processes disclosed in Cashman et al thus include both bulk polymerization and solution polymerization processes in which the reaction is run at temperatures of up to 250.degree. F., but preferably between about 100.degree. and 200.degree. F., in the presence of an alkaline medium. This alkaline medium is essential to the Cashman et al process apparently in order to neutralize the residual acid in the first step of the Cashman et al processes, in which the fumarate is prepared. The processes disclosed in Cashman et al, however, have not proven to be commercially sufficient, and the actual commercial processes for the production of these additives have almost exclusively been conducted in the presence of a solvent, such as heptane, hexane, or cyclohexane.
Furthermore, Tutwiler et al, U.S. Pat. No. 2,936,300, discloses processes for the copolymerization of vinyl acetate with a dialkyl fumarate in which the reactants are mixed with a solvent or diluent such as white oil in the presence of peroxide catalysts, such as benzoyl peroxide, with cooling to absorb the heat of polymerization so that the reactions are run at temperatures of from 50.degree. to 125.degree. C. (122.degree. to 257.degree. F.). Also, Young et al, U.S. Pat. No. 3,507,908, discloses the copolymerization of dialkyl fumarate with vinyl esters in the presence of a trialkyl aluminum catalyst utilizing a solvent polymerization reaction. These patents are typical of those processes, such as the commercial production of the fumarate vinyl acetate copolymers, in which it has been believed that the presence of a solvent was essential thereto. This was believed necessary not only to maintain a workable viscosity, but even more importantly to act as a chain transfer agent in order to terminate these free radical catalytic reactions. It was therefore believed that the molecular weight of the copolymer produced thereby, without the presence of a solvent, would become far too great, and considerably above the desired molecular weight for these products intended for use as fuel and lubricating oil additives. It was also believed that the presence of the evaporation of the solvent was necessary so as to moderate the reaction temperatures of these exothermic reactions.
Other patents have discussed bulk polymerization processes of various kinds. These include Voss et al, U.S. Pat. No. 2,200,437, in which vinyl esters of organic acids, including vinyl acetate, are polymerized in the presence of peroxides of the fatty acids containing at least 16 carbon atoms, with the patentee contending that they unexpectedly discovered that by using such catalysts higher molecular weight polymerization products can be produced, specifically compared to the use of catalysts such as dibenzoyl peroxide and the like. In particular, in example 4 of this patent the vinyl acetate is copolymerized with maleic acid dimethyl ester with oleic acid peroxide at 80.degree. C. (176.degree. F.). This disclosure does not mention, however, the fumarates as a candidate for any of the copolymerization reactions thereof. The maleic acid esters of Voss et al are not, however, nearly as effective as pour point depressants as are the fumarate copolymers of the present invention. Trulacs et al, U.S. Pat. No. 4,220,744, discloses other bulk polymerization processes, in this case employing acrylic monomers and minor quantities of alpha, beta-unsaturated monomers therewith.
The search has therefore continued for commercially acceptable process for copolymerization of vinyl acetate and fumaric acid diesters for the production of these fuel and lubricating oil additives which can be conducted on a commercial scale in the absence of a solvent medium.